From patchwork Tue Jun 18 10:03:01 2024 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Paul Cercueil X-Patchwork-Id: 13702038 Received: from aposti.net (aposti.net [89.234.176.197]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 7C0DF213150; Tue, 18 Jun 2024 10:04:01 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=89.234.176.197 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1718705043; cv=none; b=jW/xUH0jAU8UHvwj78cqGgZDbHt6txSHxw6zj9+v8sDChpkjBnvwMSF40dzBKHc+b3MAAiPFPJDiSjRxRdreOD5+Fs9vt76lHUuYjy+BHkN8XBUVVPe8g8FznwYSNM4GHCzJQNXE2CpuYJH1+Gz/n9KipzFx1XyhtNNc7y+FCpI= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1718705043; c=relaxed/simple; bh=rxuxrnuLAzYnJpChC7mDsaXMHmsflaOSlgWDLcGldHA=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=mFqknFGJNvmcd4EZnmtAhH2/fdigNeLLCWIBBKQ1s8sm0+v3Xhr+Q8znVzMdx7d32T1tXkgVhox5Nc8qJa3HJ4fydmAR1m3RGdXc11TRgYqUZsYrlDKo/rMgLL3Sprw92q+sfDhMUQ2W/0e9pWeXdLSjrlUI6Kk2tM/K089NtBk= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=crapouillou.net; spf=pass smtp.mailfrom=crapouillou.net; dkim=pass (1024-bit key) header.d=crapouillou.net header.i=@crapouillou.net header.b=wleQHN+L; arc=none smtp.client-ip=89.234.176.197 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=crapouillou.net Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=crapouillou.net Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=crapouillou.net header.i=@crapouillou.net header.b="wleQHN+L" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=crapouillou.net; s=mail; t=1718704996; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=/uHGRMKk9xND9JDSJXhO37j4a+IBIelBDXj6Y7q76eE=; b=wleQHN+LHyOTHs6JuLerJ6ZqtYWdCaGlTtq72+FIoVFzZ4WDm/KCd3HJ9jYx2HhfM7fZ7u b6V5zwgB3CkAX9ZLkM0GoT4UHSlQnCsIekEWIM2Cg8+YViZch9wtu26hpbTql1owb9MzF2 lAK3YSy1wg6MhxxYumfLRE0+vy+cZAI= From: Paul Cercueil To: Jonathan Cameron , Lars-Peter Clausen , Vinod Koul , Sumit Semwal , =?utf-8?q?Christian_K=C3=B6nig?= Cc: Jonathan Corbet , Nuno Sa , linux-iio@vger.kernel.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, dmaengine@vger.kernel.org, linux-media@vger.kernel.org, dri-devel@lists.freedesktop.org, linaro-mm-sig@lists.linaro.org, Paul Cercueil Subject: [PATCH v11 6/7] Documentation: iio: Document high-speed DMABUF based API Date: Tue, 18 Jun 2024 12:03:01 +0200 Message-ID: <20240618100302.72886-7-paul@crapouillou.net> In-Reply-To: <20240618100302.72886-1-paul@crapouillou.net> References: <20240618100302.72886-1-paul@crapouillou.net> Precedence: bulk X-Mailing-List: linux-iio@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Document the new DMABUF based API. Signed-off-by: Paul Cercueil Co-developed-by: Nuno Sa Signed-off-by: Nuno Sa --- v2: - Explicitly state that the new interface is optional and is not implemented by all drivers. - The IOCTLs can now only be called on the buffer FD returned by IIO_BUFFER_GET_FD_IOCTL. - Move the page up a bit in the index since it is core stuff and not driver-specific. v3: Update the documentation to reflect the new API. v5: Use description lists for the documentation of the three new IOCTLs instead of abusing subsections. v8: Renamed dmabuf_api.rst -> iio_dmabuf_api.rst, and updated index.rst whose format changed in iio/togreg. v11: - "a IIO buffer" -> "an IIO buffer" - Add variable name in IOCTL calls --- Documentation/iio/iio_dmabuf_api.rst | 54 ++++++++++++++++++++++++++++ Documentation/iio/index.rst | 1 + 2 files changed, 55 insertions(+) create mode 100644 Documentation/iio/iio_dmabuf_api.rst diff --git a/Documentation/iio/iio_dmabuf_api.rst b/Documentation/iio/iio_dmabuf_api.rst new file mode 100644 index 000000000000..ad0177c3fef2 --- /dev/null +++ b/Documentation/iio/iio_dmabuf_api.rst @@ -0,0 +1,54 @@ +.. SPDX-License-Identifier: GPL-2.0 + +=================================== +High-speed DMABUF interface for IIO +=================================== + +1. Overview +=========== + +The Industrial I/O subsystem supports access to buffers through a +file-based interface, with read() and write() access calls through the +IIO device's dev node. + +It additionally supports a DMABUF based interface, where the userspace +can attach DMABUF objects (externally created) to an IIO buffer, and +subsequently use them for data transfers. + +A userspace application can then use this interface to share DMABUF +objects between several interfaces, allowing it to transfer data in a +zero-copy fashion, for instance between IIO and the USB stack. + +The userspace application can also memory-map the DMABUF objects, and +access the sample data directly. The advantage of doing this vs. the +read() interface is that it avoids an extra copy of the data between the +kernel and userspace. This is particularly useful for high-speed devices +which produce several megabytes or even gigabytes of data per second. +It does however increase the userspace-kernelspace synchronization +overhead, as the DMA_BUF_SYNC_START and DMA_BUF_SYNC_END IOCTLs have to +be used for data integrity. + +2. User API +=========== + +As part of this interface, three new IOCTLs have been added. These three +IOCTLs have to be performed on the IIO buffer's file descriptor, +obtained using the IIO_BUFFER_GET_FD_IOCTL() ioctl. + + ``IIO_BUFFER_DMABUF_ATTACH_IOCTL(int fd)`` + Attach the DMABUF object, identified by its file descriptor, to the + IIO buffer. Returns zero on success, and a negative errno value on + error. + + ``IIO_BUFFER_DMABUF_DETACH_IOCTL(int fd)`` + Detach the given DMABUF object, identified by its file descriptor, + from the IIO buffer. Returns zero on success, and a negative errno + value on error. + + Note that closing the IIO buffer's file descriptor will + automatically detach all previously attached DMABUF objects. + + ``IIO_BUFFER_DMABUF_ENQUEUE_IOCTL(struct iio_dmabuf *iio_dmabuf)`` + Enqueue a previously attached DMABUF object to the buffer queue. + Enqueued DMABUFs will be read from (if output buffer) or written to + (if input buffer) as long as the buffer is enabled. diff --git a/Documentation/iio/index.rst b/Documentation/iio/index.rst index 4c13bfa2865c..9cb4c50cb20d 100644 --- a/Documentation/iio/index.rst +++ b/Documentation/iio/index.rst @@ -9,6 +9,7 @@ Industrial I/O iio_configfs iio_devbuf + iio_dmabuf_api iio_tools Industrial I/O Kernel Drivers